1. Field of the Invention
The present invention relates to a cleaning apparatus designed to remove residues such as fats and oils, chemical substances, medicines and the like in piping by movement of a pig.
2. Description of the Prior Art
Japanese Patent Laid-open Publication No. 62-38040 (38040/1987) discloses an example of a cleaning apparatus to remove residues from piping, which includes a cylindrical body constituting a catcher to stop a pig projected from a launcher, and a separating mechanism having a jet port. In the cleaning apparatus, a compressed fluid is discharged through the jet port to thereby stop the pig and, the stopped pig is removed after the cylindrical body is opened separately by the separating mechanism.
Another example of the above type apparatus is described in Japanese Utility Model Laid-open Publication No. 59-142085 (142085/1984), which is provided with a launcher and a catcher, wherein an outlet of a high pressure gas in the catcher is positioned so as to be clogged by a pig.
Meanwhile, in a pig sensing apparatus revealed in the Japanese Utility Model Laid-open Publication No. 62-144593 (144593/1987), a sensing rod with a sensing plate at the front end thereof is slidably mounted in a hole formed in a blind patch at the end part of a pipe, and a branch pipe is provided at the end of the piping to let out the discharged matter.
The pig is moved only in one direction in the conventional apparatuses mentioned above. Therefore, not only the removing efficiency of residues adhered to the wall of the piping is poor, but also it is annoyingly necessary to remove the pig sent to the catcher and reload the pig in the launcher every time the pig is projected from the launcher, resulting in complication of the cleaning work.
According to an apparatus disclosed in the Japanese Patent Laid-open Publication No. 62-87836 (87836/1987), a speed of the pig movement is controlled so that it can be stopped at optional positions. Specifically, the pig has a through-hole bored in the main body thereof, a valve plate for opening/closing the through-hole and an actuator for activating the valve plate. The arrangement is not advantageous, however, since it requires use of the pig of the complicated structure as above.
On the other hand, the Japanese Patent Laid-open Publication No. 2-95487 (95487/1990) shows a cleaning method, where a plurality of pigs are inserted into piping while a solvent is sealed between the pigs, to thereby clean the interior of the piping as the pigs are run through the piping. In this cleaning method, since a solvent is sealed in the plurality of pigs, the cleaning work becomes intricate, with a fear that the piping will be contaminated with the solvent thereinside. Therefore, the cleaning method is limited only to use in a transportation pipeline for crude oil or heavy oil.
Since it is necessary for the pig to run in the entire piping between the launcher and catcher according to the conventional apparatuses or method as above, it is impossible to clean only a part of the piping. In the case, for example, where branch pipes are connected at a plurality of points of a main pipe connecting the launcher and catcher and each branch pipe is connected with a tank, if a liquid is transported into and stored in a first tank at the side of the launcher, the pig must be moved within the entire main piping to clean the main piping totally although the main piping at the lower side of the stream of a first branch pipe need not necessarily be cleaned. In such a case as above, the residue is transferred to a second branch pipe located at the lower side of the stream relative to the first branch pipe in accordance with the running of the pig. Consequently, when a liquid is supplied to a second tank at the lower side of the stream relative to the first branch pipe through the cleaned main piping and the second branch pipe, the liquid in the second tank may be contaminated with the residue in the second branch pipe.
In the meantime, if the conventional apparatus or method described above is to be applied to a duct system constituting main piping and branch pipes branching from the main piping to tanks, the pig may be sometimes erroneously brought into the branch pipe. That is, as the pig is an elastic body transferred by a high pressure fluid, the pig may be pressed into the tank through the branch pipe during cleaning particularly when a liquid is transported and stored in a plurality of tanks. Therefore, the pig must be removed from the tank and mounted to the launcher again. This makes the cleaning work troublesome.